The information carrying capacity of any data network is limited by, among other things, its effective bandwidth. Limitations in available bandwidth, resulting from technical limitations of the processing and transmission elements (e.g. transmission line limitations), from government limitations (e.g. limited RF spectrum allocation), or otherwise, restrict the amount of information which can be carried by the related system. This may result in a limitation on the quantity or quality (or both) of the services which may be provided by the system, often requiring compromises or tradeoffs.
Transmission of television programming to home viewers has long been subject to the these limitations and tradeoffs. Terrestrial RF broadcasts are limited in a given locality to a few frequency bands (channels) allocated by government authority for television transmission, and selected to be noninterfering over the limited range of the transmission. The frequency band allocated to each channel was selected to accommodate the then-standard transmission scheme employed (e.g. NTSC in the United States), and to minimize or avoid out-of-band interference. Although additional frequencies (e.g. UHF in the United States) were later allocated, restrictions on available RF spectrum have long limited the number of programs which could be made available to the consumer.
Distribution of program material via cable networks provided additional bandwidth to broadcasters (i.e. cable operators), overcoming in part the restriction imposed by scarcity of available RF spectrum. However, cable systems are technically limited to the useable bandwidth of the network, including the transmission line and associated electronics.
Advances in signal processing technology have permitted more programming information, improved quality, and new services (e.g. data services) to be transmitted within a given available bandwidth. For example, digital processing of both video and audio signals, together with advances in encoding and compression techniques (e.g. MPEG-2), have permitted a reduction in the bandwidth required for transmission of video and audio signals of acceptable quality, and/or transmission of higher quality video and audio signals. Together with advances in the associated transmission and reception equipment allowing greater utilization of available spectrum, a dramatic increase in the amount of user programming that can be transmitted over a given medium is possible. In addition, systems have been developed to utilize alternative delivery systems and other portions of the RF spectrum. For example, direct broadcast satellite (DBS) systems provide entertainment and information broadcasts directly to consumers in some cases by means of high power satellite transponders and small (e.g. 18-inch) consumer receiving dishes. Although one such system is today capable of transmitting over 225 channels of video, audio and/or data programming at higher quality levels than previously known there remains a desire to provide additional transmission capability and to fully utilize all available bandwidth for benefit of the consumer.
Distribution systems, whether broadcast (satellite or terrestrial), coaxial cable, optical, or otherwise, typically provide a plurality of accessible broadcast resources. In an early model, a terrestrial television broadcast system included a number of individual channels or frequency bands, selectable by the consumer. Taking the television system as a whole, each channel available in a given locality provided a broadcast resource accessible by the users in that region and capable of carrying a single video/audio program. Similar frequency division multiplexing on known analog cable systems provides a generally larger number of broadcast resources in the system, again each typically carrying a single program including both video and audio, selectable as a viewer channel. In a digital DBS system, frequency and polarization division multiplexing (e.g. multiple transponders operating with distinct frequencies and with two polarizations) and data packet multiplexing (e.g. within a given frequency) may be used. In this context, each individually addressable bitstream (i.e. each individual packet virtual circuit on each selectable frequency and phase) may be considered as a separate “broadcast resource.” Where different satellite locations or different delivery media are also employed in an extended system, selection of the desired satellite and transmission media, etc., is also part of identifying an individual broadcast resource.
A broadcast service will therefore have available to it a limited number of broadcast resources. If the quality of individual transmissions can be acceptably reduced, additional broadcast resources might be supported within a given RF spectrum allocation. However, the number of broadcast resources available for transmitting high quality video, audio and data programming remains limited.
A broadcaster or service provider desires to transmit to its customers (e.g. subscribers) the maximum number of programs possible utilizing the available transmission system, at the highest relative quality. As used herein, “programs” shall include television programming, audio programs, and/or data transmission of various types (e.g. software, control codes, multimedia content, digitized pictures, data, etc.). A program may include more than one form of data, such as video and one or more audio, and in some embodiments, associated data. Each of these data streams may, in preferred embodiments, be transmitted over separate broadcast resources.
A large number of content providers exist today and make available to broadcasters one or more content streams comprising programs and related content (e.g. program IDs, commercials, etc.). Many of these streams are continuous or substantially continuous, and are distributed by the content provider through various distribution media (e.g. satellite, cable, or prerecorded media) to, among other potential recipients, other broadcast services for retransmission to their viewers. For example, numerous regional sports networks exist which assemble program streams containing sporting events, often with sports-related “filler” in the times between individual sporting events.
Although content providers often generate original programs (e.g. by covering a live sporting event), it is common in the industry for one content provider to purchase programs or filler from another content provider. For example, a sports network might purchase retransmission rights to a sporting event being covered by another service provider. In these cases, the purchasing provider receives a program feed from the distribution medium (e.g. satellite) utilized by the originating provider, then retransmits this signal to its customers (e.g. cable system operators for further retransmission to consumers, or directly to consumers). The purchasing provider may insert its own commercials or identity, or may elect to use the purchased feed in its “raw” form. Often several service providers will purchase and carry the same programming originated by another provider.
A multi-channel broadcast system will typically purchase a number of input program streams from a number of content providers, for retransmission to viewers or subscribers of that system. In a digital transmission system, each individual program stream can be viewed as a continuous input data stream, where the data represents video, audio, or other (e.g. multimedia or data) information, and will be referred to herein as an “input data stream.” A given program may comprise one or more than one input data streams (e.g. one or more video inputs, one or more associated audio inputs, and associated data relating to the program content). Transmitting a given number of input data streams to a number of viewers, such that each data stream is potentially available to users at all times, has typically required at least an equal number of broadcast resources.
In particular, at the transmission end each input data stream is typically assigned to an available broadcast resource. Each input data stream is therefore allocated or “mapped” to a unique broadcast resource. The correspondence matrix identifying the input stream-to-broadcast resource relationships may be considered as a “map”. Because the map used at the transmission end is remote from the user (e.g. subscriber), it will be referred to herein as a “remote” map.
At the receiving end, a similar map has been used to allocate the data streams received from the broadcast resources to unique, selectable outputs. Each individual output bitstream, corresponding to a particular broadcast resource bitstream, may be referred to as an “output data stream.” When a user selects a particular channel (e.g. channel 101) they expect to receive a particular program at a particular time. The receiving device accomplishes this by maintaining a complimentary receiver or “local” map which specifies the correspondence between broadcast resources and selectable outputs. In some instances, where the desired output consists of information carried over just one broadcast resource, the local map will specify correspondence between that broadcast resource and the selected output, which will consist of a single output data stream. For example, if the video and audio components of a program are encoded into a single input data stream, then selection of a program or viewer channel requires mapping of only one data stream, with the components being separated by other processors. In other instances (e.g. a movie having one or more video options, a plurality of selectable high quality audio, and/or optional related data), selection of a desired output may require mapping multiple output data streams to the corresponding broadcast resources. In these instances, the user selects a desired “viewer channel” (e.g. channel 101) and makes any optional selections (e.g. alternate audio), and the local map identifies the necessary output data streams and maps them to appropriate broadcast resources. These output data streams may be directed to an appropriate processing or performance device, such as (without limitation) a television display, audio processor, or computer. Where options are available (e.g. alternate audio), the selected option may be mapped to an output corresponding to a related processor based on a user select input, or all of the options may be mapped to a processor which itself isolates the appropriate output. In specific embodiments, components of different programs (e.g. video from a first program and audio from a different source) may be locally mapped to an output viewer channel, thereby creating a hybrid derived output.
It is important that both the remote and local maps correspond at any given time, so that selection by the user of a viewer channel will map the receiving circuitry to the correct broadcast resource(s) which, in turn, are mapped to the input data stream(s) desired by the user. It is known to modify the allocation maps from time to time. This may be done, for example, when a broadcast resource becomes unavailable, or when a reallocation of bandwidth provided by individual resources is required, such as when new input data streams are added to, or old ones removed from, a system. Such map changes have been infrequent, however, typically one to three times per day.
Technology also exists to locally generate derivative output data streams or viewer channels which do not correspond to any single input data stream. For example, a local processor may map a particular viewer channel to a first set of one or more broadcast resources during a first time period, then map that viewer channel to a different set of broadcast resources during a subsequent time period. In this manner, a processor has been able to provide viewers with a greater number of viewer channels than the number actually broadcast.
For purposes of the ensuing description and claims, the following notation convention may be useful. The numerical correspondence between individual input data streams and individual broadcast resources (related to the remote map), and the numerical correspondence between those broadcast resources and individual output data streams (related to the local map), may be given as IN:BR:OUT, where IN equals the number of discrete input data streams, BR represents the number of discrete broadcast resources, and OUT represents the number of discrete output data streams. In the simplest 1:1:1 correspondence, n input data streams are mapped to n broadcast resources, which are in turn mapped to n output data streams, or n:n:n. As previously noted, it is also known to generate derivative channels, which may be represented as n:n:n+x correspondence or mapping, where n and x are integers greater than or equal to one. In this example, although a 1:1 correspondence exists between input data streams and broadcast resources, a 1:>1 mapping is performed by the local map, resulting in x derivative output channels.
Although revision of the maps to accommodate infrequent changes in the input data streams or active broadcast resources, and n:n:n+x mapping to locally generate derivative channels, have provided a useful degree of flexibility in the operation of existing systems (e.g. high capacity DBS), it would be useful to reduce the amount of bandwidth required to carry desired programming, thereby allowing additional services and/or higher quality services to be carried by the same broadcast resources.
It is also known that certain control and configuration information must be transmitted, in addition to the desired input data streams. Using channel maps introduces difficulties in generating and maintaining an accurate local map which reflects the current utilization of broadcast resources. Changes in the utilization of resources over time require the local map to be updated, typically by transmitting or downloading a new map to a viewer's receiver such as (for a typical DBS system) an integrated receiver/decoder (IRD). For a system having a large number of channels (i.e. 225 or more), the local map may comprise a matrix of several thousand bytes of data listing the appropriate broadcast resources for each viewer channel, for one or more time periods. Such “overhead” data transmission requires bandwidth which is therefore not available for delivery of desired consumer services. In the case of infrequent map updates, this overhead has been tolerable, although not desired. If the complexity or size of the local map were increased, or if revisions to the local map were frequent, the amount of overhead bandwidth required could become quite large.
Transmission of local map data also requires time, the amount of which depends on the amount of map data and the allocated effective baud rate. Other sources of delay in generating and activating an updated map may also exist. For example, an IRD ordinarily continues to use a map until it determines the complete transmission of a more recent, updated map. Typically the IRD checks for the existence of an updated map at only predetermined intervals. Thus, another source of delay is introduced in activating a new local map.
The time delays involved with transmitting updated local maps to IRDs have also made maintaining updated maps cumbersome. The transmission of updated maps has thus been typically limited to a fixed number of predetermined times during the broadcast day, e.g. two or three times per day. Changes in the utilization of broadcast resources are therefore limited by the practical ability to update the local map. Improved flexibility in updating channel maps would allow greater flexibility in maximizing the utilization of broadcast resources.
U.S. Pat. No. 5,886,995 has provided a system whereby broadcast resources are conserved. In the '995 patent, a program guide system is used to create the look and feel of a unique local channel for each local market. The local map appears to have the identifier of the local channel but, the same video from another channel is used in place of the actual local channel feed. One drawback to such a system is that the local channel identifier such as logo displays which are broadcast from the local channels are not displayed on screen. Local channels may therefore object to substituting a national feed for their local feed during particular times. Another problem with such systems is that the local emergency messaging system that provides information such as severe weather alerts may also be eliminated during time periods with redundant signals. U. S. Pat. No. 5,886,995 is hereby incorporated by reference.
It would therefore be desirable to provide a broadcast system that reduces redundant signals so that further content may be provided without losing local identity.